A method, non-transitory computer readable medium, and productivity assessment computing device that identifies entities present in frames of a video. Entity movement across the frames is plotted to obtain a trajectory of the entities. Interactions of one or more of the entities in each of the frames are identified. A unique sequence encoding is generated for subtasks performed by each of the entities. One of the subtasks is classified as a waste subtask based on one or more of the interactions corresponding to the one of the subtasks and the trajectory and a type of each of the entities associated with the interactions. The sequence encodings of the one of the subtasks are correlated with a number of frames per second of the video to determine waste duration value(s) for a task and the waste duration value(s) are output.